tool_operate: Show HTTPS-Proxy options on CURLE_SSL_CACERT

When CURLE_SSL_CACERT occurs the tool shows a lengthy error message to
the user explaining possible solutions such as --cacert and --insecure.

This change appends to that message similar options --proxy-cacert and
--proxy-insecure when there's a specified HTTPS proxy.

Closes https://github.com/curl/curl/issues/1258